1. Field of the Invention
The present invention relates to an improved molding process and apparatus. More particularly, the present invention relates to an improved molding process and apparatus for molding a gasket to a filter element.
2. Description of the Prior Art
Rectangular or cylindrical filter elements used in filter assemblies for filtering fluids, such as ambient air, are frequently configured with a rectangular or cylindrical filter media in which fluid being filtered passes axially or radially through the filter media either from, or to, a hollow central core which is plugged at one end. In order to appropriately mount the filter media within a filter housing of the filter assembly, the filter media is frequently provided with a radially projecting, gasket for sealing the filter media with respect to inlet and outlet openings of the filter housing.
A conventional practice in forming the sealing gasket of the filter elements is to expand within a mold cavity foamable material such as polyurethane produced by a mixture of polyol and isocyanate. When using this process, the expanding material produces flash between upper and lower mold halves. The flash must be trimmed and vacuumed off prior to sale of the filter element; otherwise, the flash may become dislodged during installation or operation. If the flash is sucked against the filter media, the media""s efficiency is reduced. There is also the chance of loose flash being transferred into the engine or other machine on which the filter employing the media is installed and meant to protect.
Another difficulty which arises when forming such annular seals is the occurrence of pits or other discontinuities in the surface of the gasket due to air or other gas bubbles being trapped as the material from which the gasket is formed expands into engagement with the surface of the top mold. In addition to presenting an unfinished appearance, these defects can on occasion result in a leaking seal which can allow at least small debris to be sucked around the gasket into the engine. In addition, the strength of the gasket may be compromised if large air bubbles are trapped in the foam material as it expands.
The present invention provides a new and improved molding apparatus for forming a sealing gasket on a filter media. The molding apparatus comprises of a first, or bottom, mold component and a second, or top, mold component each provided with a corresponding mold surface. The first and second mold components are substantially rectangular in cross section and cooperate to define a mold cavity positioned around a filter media formed by their respective mold surfaces and adapted to receive an expandable material forming the sealing gasket.
The mold cavity includes a substantially semi-spherical ridge portion having an apex. The ridge portion defines a rib of the sealing gasket of the filter element. The ridge portion of the mold cavity is formed by both the first and second mold components abutting each other at the apex of the ridge portion of the mold cavity along a mold line oriented at an angle to a central axis of symmetry of the mold apparatus. Moreover, the mold surfaces of the mold components have upwardly sloping ramp surfaces.
The sealing gasket is formed by molding the expandable material in the mold cavity defined by first and second mold components. As the material expands, a portion of the material is accumulated in the ridge portion of the mold cavity while allowing the residual gas and air remaining after the expansion of the expandable material escape between the first mold component and the second mold component as they meet at the apex of the ridge portion along the inclined mold line, thus eliminating a peripheral flash formed on the sealing gasket which must subsequently be trimmed.
Furthermore, the invention provides venting the cavity through the filter media as the gasket forming material expands in a way that air and gas in the mold cavity does not become trapped in the media and form blemishes and discontinuities on an outer surface of the sealing gasket. The effectiveness of the venting step is enhanced by providing the upwardly sloping ramp surfaces in the first and second mold components adjacent to the location of the filter media which define a surface which assists in conveying air and gas from the mold cavity and through the filter media as the material expands within the mold cavity to form the sealing gasket. Thus, chances are minimized that the sealing gasket will have imperfections or blemishes therein.
Preferably, the material for forming the sealing gasket is open foam polyurethane formed by mixing polyol and isocyanate. However, any other appropriate resilient material known in the art is within the scope of the present invention.
Therefore, the molding apparatus in accordance with the present invention provides a filter element with a sealing gasket free of the peripheral flash, imperfections and blemishes.
Upon further study of the specification and appended claims, further features and advantages of this invention will become apparent to those skilled in the art.